This invention relates to bioderived plasticizers for use with biopolymers. As used herein the term “bioderived” means made from plant-made molecules that are either directly expressed from plants, such as sugars, starches or fats, or fermented from plant-made molecules, such as sugars, starches, or fats. As used herein the term “biopolymers” means polymers made from plant derived molecules. The disclosed bioderived plasticizers improve the flexibility of the biopolymers without adversely affecting the Young's Modulus or bleeding out at high temperature or over time, such as in storage.
Polylactic acid (PLA) is becoming a widely used biomaterial due to its biocompatibility, biodegradability and sustainability. Polylactic acid is expected to expand its application base because the raw material L-lactic acid can be inexpensively produced in a large scale by a fermentation process, degradation velocity of polylactic acid is high in the compost, and polylactic acid is excellent in resistance to fungus and protection of foods from contamination of odor and color. Preparation of high molecular weight lactic acid polymers can be conducted by (1) ring-opening polymerization (ROP) of the dehydrated ring-formed dimer or dilactide, (2) polycondensation and manipulation of the equilibrium between lactic acid and the polylactide by removal of the reaction water using drying agents, or (3) polycondensation and linking of lactic acid prepolymers. Polylactic acid has the following general formula:

Polylactic acid has high rigidity and is unsuited for applications that require flexibility and toughness, such as agricultural multi-films, food packaging bags, garbage bags and other polymeric films, rigid durables such as computer casings and automotive parts and some packaging.
Generally known techniques for making polylactic acid flexible are (1) addition of a plasticizer, (2) copolymerization and (3) blending of flexible polymers. Though these techniques generally improve the flexibility of the polylactic acid, there are problems associated with their use. Technique (1) creates a material that generally has the properties needed for flexible films, but the production usually requires a large layout of capital which limits its use to large manufacturers of base resin. Technique (2) also “softens” polyesters like lactic acid or polyhydroxybutyrates (PHB), but the plasticizers tend to bleed out over time. Another issue is that techniques (1) and (2) lower the glass transition temperature of the resin composition but this also changes the physical properties such as making the material less strong as seen in a lowering of the tensile modulus.
Technique (3) usually involves blending a flexible and biodegradable resin. Examples include polybutylene terephthalate-adipic acid, polybutylene succinate, polyethylene succinate, and polycaprolactone. In some cases, additional plasticizers such as citrus esters are used in addition to the polymeric plasticizers (U.S. Pat. No. 7,166,654). Examples of these resins have been disclosed in BASF U.S. Pat. Nos. 5,817,721, 5,889,135, and 6,018,004, Eastman Chemical U.S. Pat. Nos. 6,342,304, 6,592,913, and 6,441,126, and Japanese Patent HEI 8-245866 and HEI 9-111107, which are incorporated herein by reference.
Linear polyesters of diols and diacids have been used as plasticizers for polymers from PVC to highly crystalline polyesters of polycarbonate, polylactic acid, and other polyhydroxyalkanoates. Several of these materials have been made commercially available including BASF Ecoflex, Eastman Chemical's EastStar Bio, and Showa High Polymer Company's Bionolle U.S. Pat. No. 5,324,794. Blends made with these materials tend to have reduced modulus and they are not optically clear.
However, in order to provide sufficient flexibility (an elastic modulus of 1,000 MPa or less) for polylactic acid, the technique requires the addition of a large amount of the flexible resin, for example, 60% by weight or more polybutylene succinate. This impairs certain desirable characteristics of polylactic acid, such as the Young's Modulus.
It would be an advancement in the art to provide a polymeric plasticizer that improves the flexibility of the biodegradable polymer without adversely affecting the Young's Modulus.
It would be a further advancement in the art to provide a plasticizing agent that can be blended into biodegradable polymers as well as petrochemically derived polyolefins to produce products, such as films used for garbage bags, packaging materials, injection molded parts, bottles and the like, that have excellent toughness and flexibility at low plasticizer concentrations without sacrificing physical properties such as the Young's Modulus.
It would be yet another advancement in the art to provide a polymeric plasticizer that may be blended with PLA, other polyesters such as PHAs, HIPS, ABS, polystyrene, or polyolefins such as polyethylenes, polypropylene, or copolymers of the polyethylene that shows improved compatibility and outstanding resistance to bleeding out at high temperature or over time.
It would be still another advancement in the art to provide a polymeric plasticizer that can be used grafted to the backbone of polyolefins using an unsaturation functionality of the copolymer plasticizer.
It would be a further advancement in the art to provide a polymeric plasticizer that can be used as a compatibilizer or an emulsifier for polyolefin/polyester blends and/or polyolefin/starch blends.